In modern communications and information technology, optoelectronic devices play increasingly important roles. For example, they form interfaces between the communication carriers (optical fibers) and the processing stations which largely use semiconductor electronics.
Optoelectronic devices convert optical signals into electrical signals and, conversely, convert electrical signals to optical signals in the form of photons of light emitted from the component.
While the greater part of microelectronic circuitry to date has been based upon silicon technology, in the field dealing with light/electrical signals, i.e. optoelectronic components, so called III/V or III-V semiconductor elements have been employed for lasers, light emitting diodes (LED) and the like. Group III/V or III-V semiconductors are semiconductors having as one element at least one member of group IIIA of the Periodic Table (e.g. Al, Ga, In, Tl) and as a second element at least one member of group VA of the Periodic Table (e.g. P, As, Sb, Bi).
With respect to state of the art, reference can be made to Optics and Spectroscopy, 26 (1969), page 176 and J. Appl. Phys. 44 (1973), pages 5029-5030. Here a system is described in which a fluoride layer, for example CaF.sub.2 and CdF.sub.2 is doped with rare-earth elements such as Tb or Gd.
The reason for this is that the important electron transitions between conduction and valence bands, in the case of silicon, by contrast to the transitions in many III/V semiconductors, do not show luminescence.
With respect to state of the art, reference can be made to Optics and Spectroscopy, 26 (1969), page 176 and J. Appl. Phys. 44 (1973), pages 5029-5030. Here a systems is described in which a fluoride layer, for example CaF.sub.2 and CdF.sub.2 is doped with rare-earth elements such as Tb or Gd.
The rare-earth spectral line associated with a doping with lanthanides, i.e. 4f ions, has light-emitting advantages over the emission line of a III/V semiconductor light-emitting diode or a laser since the core-level emission line of the rear earth is sharper than the valence band generated broader laser line generated by a valence bond transition. Furthermore, as a result of the doping with lanthanides, problems with respect to thermal instabilities are avoided.
The 4f transition is excited in electronic applications by means of cathodo-luminescence, by impact ionization during current flow across two contacts in diode configurations or by light irradiation, for example, by means of a semiconductor laser which has its emission line corresponding to the excitation energy of the intra-f-shell transitions.
The recombination of the electron-hole pairs generated by such excitation in rare-earth ions gives rise to the emission of an energetic, relatively sharp spectral line.